It is the ultimate purpose of the proposed studies to determine whether vascular obstruction resulting from hemagglutination or other occlusive phenomena may be a cause of death in sudden infant death syndrome (SIDS). Thus, the project has two major thrusts: (1) investigation of the immunocompetence of SIDS victims, and (2) studies of infectious agents presumed to be responsible for the mechanism. Determination of the cellular and humoral immune system reactivity will rely primarily on lymphocyte transformation studies using pokeweed mitogen, phytohemagglutinin, asdlvarious viral antigens as inducing agents. Sermu concentrations of IgG, IgA, IgM, and IgE will be measured as will antivirus antibody levels. Immunofluorescence will be used to seek the above listed immunoglobulins in pulmonary tissue. Viruses will be sought in SIDS and control cases using cultures of material obtained as soon after death as possible as well as electron microscopy of this lung tissue. At the time of complete autopsy, bronchiolar washings will be obtained for further culture studies, and samples of lung for immunofluorescence will be frozen at minus 70 degrees C. Fluorescein labeled antisera will be used to search for virus particles or cells infected by viruses. Oxygen tensions will be measured in blood obtained on receipt of infants for autopsy. An infectious disease model will be sought and studies using infant or immunosuppressed rats and an adenovirus with potential for agglutination of host erythrocytes.